About this calculator
Total drop for a drain or waste pipe at a given gradient, so you can set invert levels at each end.
How it’s calculated
Fall = length ÷ gradient ratio. 1:40 = 2.5%, 25 mm per metre.
Worked example
With these inputs:
- Pipe run length
- 12 m
- Gradient
- 1:60 (1.65%)
the result is:
- Total fall
- 200 mm
- Gradient
- 1:60 = 1.67%
- Angle
- 0.95°
- Fall per metre
- 17 mm
Tips from the trade
- AS/NZS 3500.2 minimum grades for sanitary drains are about 1:40 (2.5%) for DN 65 and smaller, 1:60 (1.65%) for DN 80 and DN 100, and 1:100 (1%) for DN 150. Drainage work must be done by a licensed plumber.
- Too steep can be as bad as too flat: water outruns the solids.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the NCC and Australian Standards before ordering.